1. Field of the Invention
The present invention relates to disk drives for computer systems. More particularly, the present invention relates to a disk drive comprising a motor driver IC employing a serial interface for initiating the transmission of real-time status data to a controller IC.
2. Description of the Prior Art
FIG. 1 shows a prior art disk drive 2 comprising a disk 4 rotated by a spindle motor 6 while a head 8 is actuated radially over the disk 4 in order to write data in concentric data tracks. The spindle motor 6 typically comprises a three-phase brushless DC motor having three windings that must be commutated in an appropriate sequence to achieve a desired spin speed. The disk drive 2 comprises a closed-loop servo control system which monitors the angular position of the spindle motor in order to commutate the windings at the appropriate time. One known method for determining the spindle motor""s angular position is to monitor zero-crossings in the back EMF (BEMF) voltage generated by the three windings. A BEMF detector monitors the analog BEMF voltage and generates a square wave signal indicative of the BEMF voltage crossing the zero-level threshold.
As shown in FIG. 1, a controller integrated circuit (IC) 10 communicates with a separate motor driver IC 12. The controller IC 10 comprises control logic for configuring and controlling the motor driver IC 12, and the motor driver IC 12 comprises the commutation circuitry 14 and power FET circuitry 16 for controlling the spindle motor 6. The motor driver IC 12 also comprises a BEMF detector 18 for detecting zero-crossings in the BEMF voltage 20 generated by the three windings (xcfx86A, xcfx86B, xcfx86C) in the spindle motor 6. The zero-crossing signal is transmitted to the controller IC 10 over a line 22 dedicated to transmitting the zero-crossing signal only, and the controller IC 10 processes the zero-crossing signal to generate a spindle clock signal transmitted to the motor driver IC 12 over another line 24 dedicated to transmitting the spindle clock signal only. The spindle clock signal cycles the commutation circuitry 16 at the appropriate time. The motor driver IC 12 may also comprise a shock detector 26 for generating a shock detect signal transmitted to the controller IC 10 over yet another line 28 dedicated to transmitting the shock detect signal only. The controller IC 10 may respond to the shock detect signal by inhibiting a write operation. The motor driver IC 12 comprises a half-duplex serial interface 30 for receiving control data from the controller IC 10 and for sending data to the controller IC 10 when requested by the controller IC 10.
Using a dedicated line to transmit the zero-crossing signal from the motor IC to the controller IC minimizes jitter which would otherwise degrade performance of the spindle motor control. However, it is also desirable to minimize the pin count of the motor driver IC as well as the controller IC in order to reduce the packaging cost. There is, therefore, a need to reduce the pin count with respect to the signals transmitted between the controller IC and the motor driver IC while minimizing jitter in the BEMF zero-crossing signal.
The present invention may be regarded as a disk drive comprising a disk, a head actuated radially over the disk, a spindle motor for rotating the disk, a controller integrated circuit (IC) for generating spindle motor control data, and a motor driver IC. The motor driver IC comprises commutation circuitry for commutating the spindle motor, a status register for storing real-time status data associated with operation of the motor driver IC, and a serial interface for receiving the spindle motor control data from the controller IC and for initiating a transfer of the real-time status data to the controller IC.
In one embodiment, the serial interface initiates the transfer of the real-time status data to the controller IC when the real-time status is modified by the motor driver IC. In another embodiment, the motor driver IC further comprises a back EMF (BEMF) detector responsive to a plurality of BEMF signals generated by the spindle motor. The BEMF detector generates a BEMF zero-crossing signal indicative of at least one of the BEMF signals crossing a predetermined threshold, wherein the real-time status data represents the BEMF zero-crossing signal. In one embodiment, the serial interface delays the transfer of the real-time status data for a predetermined transmission interval in order to minimize jitter in the BEMF zero-crossing signal. In yet another embodiment, the motor driver IC further comprises a shock detector for detecting an external shock to the disk drive and for generating a shock detect signal, wherein the real-time status data comprises the shock detect signal. In still another embodiment, the spindle motor control data comprises data representing a first edge of a spindle clock, the spindle clock for cycling the commutation circuitry, and the motor driver IC comprises a timer restarted by receipt of the spindle motor control data representing the first edge of the spindle clock, the timer for generating a second edge of the spindle clock at the end of a timed interval.
The present invention may also be regarded as a motor driver integrated circuit (IC) for use in a disk drive comprising a disk, a head actuated radially over the disk, a spindle motor for rotating the disk, and a controller IC for generating spindle motor control data. The motor driver IC comprises commutation circuitry for commutating the spindle motor, a status register for storing real-time status data associated with operation of the motor driver IC, and a serial interface for receiving the spindle motor control data from the controller IC and for initiating a transfer of the real-time status data to the controller IC.
The present invention may also be regarded as a controller integrated circuit (IC) for connecting to a motor driver IC within in a disk drive comprising a disk, a head actuated radially over the disk, and a spindle motor for rotating the disk. The motor driver IC for controlling the spindle motor and for generating real-time status data associated with operation of the motor driver IC. The controller IC comprises a means for generating spindle motor control data, a status register for receiving the real-time status data from the motor driver IC, and a serial interface for transmitting the spindle motor control data to the motor driver IC and for receiving the real-time status data from the motor driver IC, wherein the motor driver IC initiates the transmission of the real-time status data to the controller IC.